This proposal aims to develop innovative methods for brain cancer diagnosis and therapy that will combine the strengths of neural stem cell (NSC) biology and in vivo phage display technology. The proposal is based on our prior work that demonstrated a remarkable, apparently "magnetic" attraction of NSCs to glioblastoma brain tumor cells. When NSCs were injected into one cerebral hemisphere, and rat or human glioblastoma tumors into the other, the NSCs migrated across the midline and headed directly to the tumor masses. When the NSCs were injected intravenously, they entered the brain and selectively targeted on the tumor. NSCs attached even to single tumor cells which were in the process of invading normal brain tissue. When NSCs were engineered to deliver toxic molecules, tumor cells were killed. New experiments will build on these results. 1. Short- and long-term effects of NSCs will be analyzed on genetically-induced natural tumors, not only on grafted tumors. 2. Optimal cell numbers and optimal route of injection into mice will be explored with mouse and human NSCs, including determination of whether a carotid intra-arterial route might be more effective than intracerebral or intravenous routes. 3. As a step toward development of diagnostic procedures of higher sensitivity, for future use in humans, NSCs will be modified to carry molecules allowing radiological visualization, so that the NSCs will serve to delineate the positions, sizes, and number of tumor masses in the brain. 4. As model "proof-of principle" experiments, NSCs will be engineered genetically to synthesize and release agents that kill dividing cancer cells and/or other agents that may induce cancer cells to differentiate into stable, quiescent glial cells that no longer endanger life. 5. To uncover the basic molecular and cell biological mechanisms controlling the "cross-talk" between NSCs and tumor cells, the powerful phage display technology, which allows identification of ligands and their receptors without preexisting data about their natures, will be used in tissue culture and in intact mice to define host and tumor ligands that react with NSC receptors and attract NSCs to the tumor, as well as the reverse - - specific receptors on brain tumor cells and on their specialized blood vessels that bind peptide ligands released by NSCs.